Abstract

Most fungi that cause human infections are free‐living saprobes and only accidental pathogens. The most prevalent mycoses
are caused by fungi that are either members of the normal human microbiota, such as species of Candida and Malassezia, or ubiquitous, exogenous fungi that are highly adapted for survival on the human host, such as species of Aspergillus and Cryptococcus. This article will summarise the aetiology, risk factors and clinical manifestations of the most common mycoses. Strategies
for their diagnoses include traditional methods of microscopy and culture, as well as the detection of fungal antigens and
antifungal antibodies, fungal deoxyribonucleic acid and structural components. Because both infectious fungi and their human
hosts are eukaryotes, they share many cellular processes and macromolecules. Consequently, it is difficult to identify targets
for antifungal drugs that do not inflict collateral damage on the patients.

Key Concepts

Superficial and cutaneous mycoses are among the most common of all communicable diseases.

Geophilic and zoophilic dermatophytes usually cause acute, inflammatory lesions that respond to topical treatment within weeks
and rarely recur. Conversely, anthropophilic dermatophytes tend to cause relatively mild, chronic lesions that may require
months or years of treatment and frequently relapse.

Subcutaneous mycoses may be caused by dozens of environmental moulds associated with vegetation and soil. These fungi are
usually acquired by contamination of minor wounds. The infections are generally chronic and rarely spread to deeper tissues.

The endemic mycoses (coccidioidomycosis, histoplasmosis, blastomycosis and paracoccidioidomycosis) are caused by dimorphic
environmental moulds and associated with distinct geographic regions.

More than 90% of endemic mycoses are caused by inhaling airborne conidia, and, in immunocompetent persons, the infections
are asymptomatic or self‐limited; however, latent, viable fungal cells may persist and subsequently reactivate to cause overt
disease. Risk factors for the manifestation of disease include compromised cell‐mediated immunity, genetic predisposition
and male gender.

Opportunistic mycoses are caused by globally distributed fungi that are either members of the human microbiota or ubiquitous
environmental fungi. These mycoses have the highest global mortality.

Most patients with HIV/AIDS develop mucosal candidiasis (e.g. thrush, oesophagitis). Those with CD4+ counts less than 100 cells μL−1 are at risk for invasive fungi, such as Cryptococcus, Aspergillus and others.

Effective treatment of invasive mycoses relies on rapid identification of the fungus, administration of the appropriate antifungal
drug and management of any underlying disease or condition.

Figure 10. Hyphae of Aspergillus fumigatus (identified after subsequent culture) in the sputum of a patient with acute pulmonary aspergillosis. Typical appearance of
vegetative hyphae produced by moulds, whether in culture or tissue, causing an infection.

Figure 11. Hyphae of Aspergillus fumigatus (identified after subsequent culture) in a histopathological section of lung tissue from a patient with pulmonary aspergillosis.

References

Ampel NM (2010) New perspectives on coccidioidomycosis. Proceedings of the American Thoracic Society 7: 181–185.